Displays which are capable of forming images of characters or patterns may be broadly broken down into two different categories, active and passive. In active displays, such as light emitting diode (LED) displays, the images are composed of individual diodes which emit their own light. Since active displays are typically characterized by high power consumption, the choice for low power applications, such as portable calculators, watches, portable radios, and pocket pagers, is typically the passive display. An example of a passive display is the liquid crystal display (LCD). Rather than emitting their own light, LCD images merely reflect or absorb light, therefore, ambient sun light or room light is normally required to view the display. When the ambient light intensity in not sufficient to illuminate the display, however, an internal supplemental illumination means is typically provided. In a simple supplemental illumination system, one or more light sources, typically incandescent lamps, are placed behind or in front of the display. One of the disadvantages of the simple supplemental illumination system is the creation of "hot spots". "Hot spots" result in poor display readability. To correct the problem of "hot spots" and to more evenly distribute the light coming from the light sources, a light guide may be positioned behind the liquid crystal display.
Previously known light guides typically comprise a slab of transparent plastic material such as polycarbon and have light sources such as LEDs positioned therewithin. The plastic material may have selected sides painted with a reflecting coating and be shaped, i.e., a "V", in order to direct more light towards the back of the LCD.
Another previously known and more complex LCD lightguide disclosed in U.S. Pat. No. 4,630,895, assigned to the assignee of the present invention, illustrates how a multi-surfaced lightguide may reduce "hot spots".
In addition to efficient backlighting, display systems generally require some type of shock absorption. This shock absorption typically has been provided by snubbers, i.e., rubber gaskets and pads, and elastomer connectors, placed against the LEDs, between the light guide and the LCD, or against the LCD opposite the light guide. The previously known display systems comprised a stand alone element including a housing.
Although the prior art light guides provide backlighting and snubbers provide shock absorption, they have one major disadvantage of thickness. Thinness is extremely important in the design of small watches, pocket calculators, pocket pagers, portable radios and any other device in which small packaging size is paramount. Therefore, it would be an improvement to decrease the impact on thickness of these two elements on the display system.
Thus, what is needed is a combination optical diffuser and snubber for backlighted liquid crystal display systems.